I find this an excellent reference.
The index is by the caterpillar's food plant, so that makes it easy for a naturalist to check quickly.
As well as the fascinating colour illustrations, there is information about the different species.
After the moth and butterfly larvae pages which fill most of the book, there is another section for larvae of other creatures that look like caterpillars, but are not. This is equally as useful because the pine sawfly, for instance, has caterpillar-like larvae which resemble pine needles and can devastate a Scots Pine in great numbers. On such occasions anyone might want to find out what the creatures are and a standard book of butterfly and moth caterpillars will be no help. This book identifies it once you keep thumbing through or focus on the Pines.